LaBerge has done a pilot study into lucid dream sex which he reported in his book Exploring the World of Lucid Dreaming.

His team used a female subject and recorded many different aspects of her physiology that would normally be affected by sexual arousal, including respiration, heart rate, vaginal muscle tone and vaginal pulse amplitude. the experiment called for her to make specific eye movement signals at the following points: when she realised she was dreaming, when she began sexual activity (in the dream), and when she reached orgasm.

She reported a lucid dream in which she flew up into the air on going lucid and circled round a university campus until she spotted a suitable man walking below, then swooped down to carry out the experiment.
Analysis of the data revealed significant correspondences between the dream activities she reported and all but one physiological measure. During the 15-second section of her physiological record which she signalled as the moment of orgasm, her vaginal muscle activity, vaginal pulse amplitude, and respiration rate reached their highest value of the night, and they also were considerably elevated in comparison to the rest of the REM period. Contrary to expectation, heart rate increased only slightly.

Since then, LaBerge and his team have carried out similar experiments with two male lucid dreamers. In both cases respiration showed striking increases in rate. Again there were no significant elevations of the heart rate. Interestingly, although both dreamers reported vividly realistic orgasms in their lucid dreams, neither actually ejaculated, in contrast to the wet dreams commonly experienced by adolescent males, which frequently are not associated with erotic dreams.